Reverberatory smelting furnace



Nov. 24, 1931. E. w. DAVIS REVERBERATORY SMELTING FURNACE Original Filed Nov. 23, 1929 4 Sheets-Sheet 2 Q/ q) BY/WJ' ATTORNEYJ Nov. 24, 1931. E, w. DAVIS 4 1,833,322

- I I REVERBERATORY SMELTING FURNACE Original Filed Nov. 23. 1929 4 Sheets-Sheet 5 INVENTOR Nov. 24, 1931. w, DAVIS 1,833,322

REVERBERATORY SMELTING FURNACE Original Filed Nov. 25, 1929 4 Sheets-Sheet 4 v =1 I WI F=== a um INVENTOR [ow/e0 /I 4145 BY/YAS' ATTORNEYS I Patented Nov. 24, 1931 I UNETED STATES PATENT oFricE EDWARD W. DAVIS, OF MINNEAPOLIS, MINNESOTA, ASSIGNOR TO DAVIS STEEL PROCESS CORPORATION, A CORPORATION OF DELAWARE REVERBERATORY SMELTING FURNACE Original application filed November 23, 1929, Serial No. 409,225. Divided and this application filed November 25, 1930.

This invention relates to reverberatory smelting furnaces and to the smelting of ores,

concentrates and similar materials therein,

and more particularly to means adapted to be used in carrying out the invention of my copIending application, Serial No. 409,225, filed ovember 23, 1929, of which the present application is a division.

According to certain methods heretofore employed in smelting finely-divided ores, the ore has been fed through openings either in the roofor side walls so as to build up piles ofore presenting extended surfaces in a position to be rapidly acted-upon by the smelting flame passing through the furnace. Various means have been employed or proposed for feeding the ore to the furnace, such as hoppers adapted to feed by gravity, and screw conveyors and plungers so positioned as to force the charge into the furnace through spaced openings in the side walls underneath and back of the previous charge.

While certain of the earlier proposals have had as an. object the gradual and uniform heating of the charge from the smelting face thereof inwardly and the feeding of fresh ore to the charge at a point remote from the smelting face and with minimum disturbance thereof, no prior worker, in so far as I am aware, has disclosed a means capable of being so operated as to attain this object; nor has any prior disclosure, with which I am familiar, indicated any appreciation ofcertain importantfactors entering into the successful operation of such smelting methods. In particular, insuflicient attention apparently has been given to the fact that in reverberatory smelting operations of this type the temperatiire conditions obtaining at various portions of the smelting face of the charge vary considerably, with the result that the charge smelts down much more rapidly in'certain places than in others, and ifthis is not taken into account disturbances of the smelting face occur.

. The present invention comprises means for feeding the charge in a layer of substantially uniform thickness through an elongated opening along one or both sides of the furnace, so as to present aninclined body of Serial No. 497,997.

charge within the furnace, and for supplying fresh materials to the charge and advancing the body of charge gradually as the face thereof is smelted, without causing material disturbance of the smelting face. The smelting face of the charge within the furnace will be coincident with an inclined plane making an angle, with the horizontal, less than the angle of repose of the charge material. By maintaining an essentially stable body of charge with a substantially unbroken smelting surface, the exposure of fresh, relatively cold ore to the action of the smelting flame is avoided and thedanger of any unreduced' ore entering the slag or metal bath is reduced to a minimum.

The invention in its broad aspects relates to a means for so feeding the charge, that the charge materials in different portions thereof will be advanced at different rates of speed corresponding to the rates at which the smelting of the charge proceeds, theieby making it possible, with proper correlation of the flame conditions in the furnace and the operation of the feeder, to maintain the inclination of the smelting face at all times below the point where relative motion will take place etween the various particles of charge on and adjacent to the surface of the ore bank.

According to one embodiment of the invention, means are provided for confining the charge at the charging opening, and for some distance in point of travel anterior thereto, in a columnar body which at the charging opening substantially conforms in cross-section to that of the charging opening, and is confined and supported on its under side by a concave supporting member adapted to move beneath the superimposed body of charge material substantially in the arc of a circle, the center of which is determined in a manner hereinafter described. Through frictional contact with the superimposed material, each particle lying in any radius drawn from the center of said circle to said concave member is thereby caused to move in a circular path aboutsuch center while maintaining its relative position in the body of the charge material substantially unchanged with respect to adjacent particles of the charge.

WVhile the present invention is of general application in the treatment of finelydivided ores and similar metalliferous materials, it is particularly applicable for use 1n carrying out the reduction of finely-dlvided iron ores and iron-containing materials with direct production therefrom of fluid iron or steel, according to the process described in my copending applicatlon Serial No. 293,491, filed July 17, 1928.

Other objects and advantages reside in certain novel features of the feeder mechanism and in certain novel features of the furnace construction, arrangement and combinatlon of parts. i

The invention will be described in further detail by reference to the accompanymg drawings in which:

Fig. I is a verticalcross-sectional view taken midway of the length of the furnace and showing the relation of the feeder mechanism to the structural features of the furnace;

tails of a preferred form of feeder mechanism;

Fig. III is a longitudinal cross-sectional .view through the center of the furnace showing the settling pocket located at one end of the hearth;

Fig. IV is a side elevation showing one feeder in position;

Fig. V is a top plan view of the furnace and feeder mechanism; and

Fig. VI is a cross-sectional view through a cylinder showing graphically the paths taken during rotation thereof by particles of a comminuted material disposed therein. 7

Referring to the drawings (Figures I and II) 10 represents the hearth of a reverberator furnace, 12 a suspended roof therefor, an 14 represents generally a preferred form of feeder mechanism associated therewith. In the construction shown, the furnace is devoid of side walls as ordinarily understood, their place being taken in operation by the slowly advancing body of charge materials' The roof 12 is brought closer to the hearth than has heretofore been the case in reverberatory practice and is of a suspended arch construction, which may, for example, comprise a air of skew-backs 16 extending Ion 'tudinafly of and at each side of the roo each belng suspended by a plurality of hanger arms 18 from I beams 20 which in turn are supported at their ends by upright members 22. The hanger arms 18 are pivoted as at 24. Tie rods 26, secured to the hanger arms as at 28, are carried through openings in blocks carried by the I beams 20. A pull is applied through the tie rods 26 against the lower ends of the hanger arms by Fig. II is a vertical cross-sectional view through one of the feeders showing the demaaaaa means of the coil springs 32, thereby tending to move the hanger arms about their,

pivots and to press the skew-backs toward one another, and to take care of contraction and expansion of the arch. The roof preferably extends some dlstance beyond the sides of the hearth over a shelf 34 extendlng along the side of the hearth.

The feeder mechanism, according to a form which has prove satisfactory in practice, consists of upright supporting members 22 and 36 joined by bracing members 38 and 40. Carried by the member 38 are links 42 and 44 pivoted at their lower ends \respectively at 46 and 48 and at their upper ends at 50 and 52 to a feeder plate 54.

A reciprocating movement is imparted to the feeder plate 54 by means of a hydraulic cylinder 56, connected through the bell crank levers 58 and 60 and the link 62 with the link 42. Disposed above the feeder plate is a hopper 64, defined by an inner wall 65 and an outer wall 67, and located in such a way that the entire bottom of the hopper is formed'by the feeder plate 54. In the drawings this hopper is shown as provided with a divider plate 66 partitioning the hopper into a large compartment 68 and a relatively small compartment 70. The. divider plate may be omitted, if desired. The bell crank levers and connecting links are so constructed as to produce only a short back and forth movement, say from to 1", depending upon the kind of charge materials being fed and the depth of the layer of charge being advanced.

It is to be'understood that, although a feed{ er mechanism of the lever type, reciprocatmg in action, is described in detail in the preceding pages of this specification, the invention is not limited to this particular mechanism as a means of attaining the desired result. The essential feature of the inven-- tion resides in providing means to occasion the uniform, progressive, movement of the body of charge downwardly and forwardly into the furnace in such a manner as will result in an undisturbed smelting face within the furnace always lying in an inclined plane making an angle with the horizontal less than that of repose of the materials of the charge under the temperature conditions obtaining. Any mechanism which would so impart a movement to the curvedfeeder plate as to attain this desired result is to be considered as within the scope of this invention.

In Fig. III is shown a novel feature of furnace construction in the form of a settling pocket 76 located at one end of the hearth. This settling pocket, set into thehearth floor, affords a reservoir for the accumulation of the fluid products of the smelting operation. It is so arranged in relation to the rest of the hearth that the fluid materials flowing down the banks of charge material collect in the trough, formed within the furnace by neeaaas the intersection of the two inclined surfaces forming the smelting faces of the ore banks, and thence pass immediately to the aforementioned settling pocket or reservoir. In this reservoir, gravity separation of the slag and reduced metal in the fluid state may be effected. Means are provided, in the form of a tap hole 7? located at the side of the furnace, for drawing off said fluid products continuously or intermittently as may be desired. By the incorporation of this novel feature, as an integral part of the general furnace construction, there is avoided any appreciable accumulation of fluid material, in the form of a slag and metal bath, on the floor of the hearth proper. made possible to operate with a maximum area. of smelting surface and thus impart a greater smelting capacity to the furnace, by increasing the area of the smelting faces exposed to the action of theismelting flame and particularly the area of those portions of the smelting faces constituting the zone of most rapid smelting.

Any suitable means for generating and passing a heating flame and gases through the furnace may be provided; In Fig. III I have shown by way of example a furnace provided with conventional air inlet and gas olftake ports 78, communicating through slag pockets 80 with passages 82 leading to regenerators, not shown. Liquid fuel burners 84 are provided adjacent the air inlet and gas otftake ports 78. y

In operation the hopper is preferably kept sufi'iciently filled to insure that the ore body seals tightly against the roof of the furnace.

The skew-back members are preferably water cooled so as better to protect the brickwork from contact with the materials of the charge. \Vhen iron ores are being reduced, it is particularly desirable to prevent contact of the iron oxide of the charge with the brickwork of the furnace, since otherwise there is a ten dency for the oxide to attack the brickwork at the temperatures of operation.

With the feeder means above described, it is possible to feed the ore gradually forward in such a way that each particle, in travelling in the confined path defined by the feeder plate 54 on the lower side and the skew-back 16 on the. upper side, moves along a line substantially constituting the arc of a circle concentric with, and, for all particles except those resting directly upon the feeder plate, of lesser diameter than that defined by the feeder plate. This is illustrated by the dotted lines a in Figures I and II, which dotted lines represent paths of travel of particles of charge at their respective indicated distances from the feeder plate from the time they pass the throat defined by the skew-back on the one side and the feeder plate on theother until they are brought to the smelting face.

' That this is so will appear obvious by ref- It is thereby erence to Fig. VI in which 6 represents a cylinder and c a body of comminuted material confined to the cross-hatched portion of the cross-sectional area of the cylinder. Let us assume that the cylinder and its contents have been rotated so that the face of the body of comminuted material indicated as H has been moved from the position indicated by the dotted lines m- 1 It will now be seen that any particles adjacent the periphery of the cylinder have moved through the distance-yy whereas the movement 1n the particles at a: is nil; also, that the relative distances travelled, or the relative rates of travel, of particles spaced at any distance from the center 00 will be proportional to their distances from such center.

The heat conditions obtaining in the furnace are normally such that the greatest amount of heat is applied to the lower portions of the inclined bank of charge material,-

and, therefore, the more rapid smelting of zones on the face of the charge have been determined for given heat conditions and the angle of repose of the charge material ascertained, the relative rate at which the materials at the lower edge or toe of the smelting face must be fed as compared with that at the upper edge is capable of accurate ascertainment. It then becomes necessary only to so locate and proportion the feeder plate that it shall describe the arc of a circle, the center of which is located atsuch distance from and in such relation to the feeder plate that the distance from the upper edge of the smelting face to such center and the distance from the feeder plate to such center, measured on a radius drawn from such center to the feeder plate and intersecting the upper edge of the smelting face, bear a relation proportionate to the relative rates of feed desired at the upper edge and the lower edge or toe of the smelting face. In this way there is prevented any undesired downward movement of the materials at the face of the charge before they are completely smelted, and thus there is avoided the exposure of raw unreduced charge materials to the smelting flame, or a mixing of such unreduced materials with the fluid metal and slag collected in the hearth.

It will be understood that a change in the rate of heat input or the distribution of the heat in the furnace will affect the relative rates of smelting of the materials in different zones of the smelting face and consequently changethe angle of theinclination of the smelting face. Such a change may in some cases be compensated for by varying the feed rate, i. e., increasing or decreasing the, re ciprocations of the feeder plate in a given period of time. For example, increasing the feed rate tends slightly to increase the relative rate of feed at the toe of the smelting face as compared with the rate of feed at the upper edge thereof. When the change in the heat input or heat distribution is too great, redesigning or relocation of the feeder plate ma be required. I

n operating with iron ores, such as Mesabi hematltes and magnetites, in the form of a mixed charge of ore, carbon and slag-forn ing materials, previously crushed or otherwise reduced to finely divided form (ore reduced to 150 mesh, flux-forming materials to 4 mesh and coal to -6 mesh), I find that the angle of repose may be taken as approximately 37 to the horizontal. p

The furnace illustrated in part in Fig. I1 was designed with a view to giving a rate of feed such that the slope of the smelting face of the charge would be'slightly less than that of the angle of repose, or that represented by the dotted line (1. In actual operation on a charge consisting of ore, coal and limestone in the proportions of 100 parts of ore, 10 parts of limestone and coal calculated to equal 80 per cent of the iron present, with furnace temperatures of approximately 1575 C. and a feed rate represented by reciprocating the feeder plate -7 inch at the rate of one complete stroke every two minutes, the smelting face assumed the inclination illustrated in Fig. II.

, It will be observed that the feeder means is of such general design that if Stratification of the materials of the charge is desired, this may be accomplished. By employing one or more divider plates such as shown in Fig. I different materials may be introduced to the several compartments of the hopper. These materials in feeding downwardly into the furnace will be maintained in clearly defined strata. As an example, it may be desirable to'partially or completely surround the ore charge with a layer of carbon. If so, coal or other suitable carbonaceous material may be introduced to the compartment 70, with ore introduced either alone or mixed with suitable amounts of reducing and fluxing materials introduced to the compartment 68. Spaced end plates 72 and 74- may also be introduced into the hopper and the spaces between the same and the ends filled with coal or other carbonaceous material. As the materials are fed downwardly and into the furnace the body of the ore issuing from the compartment 68 will remain surrounded on 'mixtures of the same'materials.

ally be advisable to feed the ore-coal-tlux charge without stratification, or merely with a layer of carbon interposed between the charge and the feeder plate on the one hand and between the charge and the end walls on the other, thus serving to protect the brickwork of the shelf 34 and the end walls against the scorifying action of the iron oxide of the charge.

The present invention is particularly appli -cable in carrying out the process of my copcnding application a (Serial No. 293,491) above mentioned, since it provides a relatively simple and practical way to bring the charge gradually and uniformly to the redu ing and carburizing stages and makes possible the carrying out of such operations under conditions such that the desired equilibrium relationship between the rates of combustion of the carbon of the charge and carburization of themetal are established and maintained.

Wherever I have used the term angle of repose in this specification, I am to be understood as meaning specifically that angle at which the material will lie quiescent in the ore bank under the conditions obtaining in the furnace. This angle changes substantially with different materials and with different In some ases a substantial crust develops at the smelting surface which makes possible the maintenance of a steeper quiescent slope on the smelting'surfaces than would be possible with such materials if no crust was formed. As above stated, it is essential that the ore particles at the smelting surface shall remain quiescent throughout the smelting operation irrespective of whether any crust is formed.

I claim:

1. Ina reverberatory furnace, in-combination a hearth, means defining an opening along a side of the hearth, and movable supporting means therebelow for feeding a charge to the furnace through said opening soas to establish and maintain a sloping body of (harge adjacent the side of the furnace with the surface of the charge that is exposed to the atmosphere in the furnace inclined to the horizontal at an angle less than that of repose of the materials of the charge.

2. In a reverberatory furnace, in combina tion a hearth, means defining an opening along a side of the hearth, a feeder disposed adjacent said opening, comprisin a chargesupporting member, and means or moving said member in an arcuate path to cause the particles of charge supported thereby to ad- Vance to the smelting zone at'rates varying directly with their distances from the center of the circle coincident with said arcuate path.

3. In a reverberatory furnace, in combination a hearth, means defining an opening along a side of the hearth, a feeder disposed adjacent said opening, comprising a chargesupporting member, a hopper above said member and discharging therefrom by gravity upon said member and means for moving said member in an arcuate path to advance the charge carried thereby and to cause the particles of charge supported thereby to ad: vance to the smeltingzon'e at rates varying directly with their distances from the center of the circle coincident with said arcuate ath. p 4. In a reverberatory furnace, in combination a hearth, means defining an opening along a side of the hearth, a feeder disposed adjacent said opening, comprising a chargesupporting member, a hopper above said member and discharging therefrom by gravity upon said member'and means for reciprocating said member in an arcuate path to ad Vance the charge carried thereby and to cause the particles of charge supported thereby to advance to the smelting zone at rates varying directly with their distances from the center of the circle coincident with said arcuate path.

. 5. In a reverberatory furnace, in combination a hearth, an arch suspended above said hearth and spaced therefrom to define. an opening along each side of the hearth, a feeder disposed adjacent each said opening, each said feeder comprising a charge-supporting member, and means for moving each of said members in an arcuate path to cause the particles of charge supported thereby to advance to the smelting zone at rates varying directly with their distances from the center of the circle coincident with said arcuate path.

6. In a reverberatory furnace, in combination a hearth means defining anv opening along a side of the hearth, a charge-supporting member disposed adjacent said opening, a hopper above said member and discharging by gravity upon said member," partition means dividing said hopper into a plurality of open-ended compartments to produce Stratification of the charge materials discharging from said hopper. and means for moving said member in a curved path to cause the particles of charge supported thereby to advance to the smelting zone at rates varying inversely with their dlstances from the surface of said member while substantially maintaining the stratification determined by said .partition means.

November, 1930.

. EDWARD W. DAVIS. 

